and many more benefits!

Find us on Facebook

GMAT Club Timer Informer

Hi GMATClubber!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

On a side note, when a question tells you a set S has numbers x,y,z - do we assume that x y z will always be different numbers? or can they be the same number, but repeated 3 times.

BELOW IS REVISED VERSION OF THIS QUESTION:

Each term of set T is a multiple of 5. Is standard deviation of T positive?

The standard deviation of a set shows how much variation there is from the mean, how widespread a given set is. So, a low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values. So, basically we can say that it in a sense measures the distance and the distance can not be negative, which means that the standard deviation of any set is greater than or equal to zero: .

Next, the standard deviation of a set is zero if and only the set consists of identical numbers (or which is the same if the set consists of only one number).

(1) Each term of set T is positive --> if T={5} then then SD=0 but if set T={5, 10} then SD>0. Not sufficient.

(2) Set T consists of one term --> any set with only one term has the standard deviation equal to zero. Sufficient.

Show Tags

11 Apr 2013, 07:18

Although it's true that this problem is tests on the concept or definition of the standard deviation, I think that I'd like to further break up my the evaluation of the two statements. Using the concept, here is how I'd solve this:

Set T = {5 * I} where I = 1, 3, 5, 7, ..., or n Question: Is SD = positive?S1: All member of T are positive.Here are some of rules:If the set consists of only one item, then SD = 0 (because mean is same as the item).If the set consists of evenly distributed number, then SD > 0So, making use of these two rule, we know that this answer is not sufficient.

S2: T consists of only one number.In this case, we know that SD is always 0. So, the answer to the question is always no.Therefore, S2 is sufficient.